Immune therapies have had some success in the treatment of metastatic cancers. However, durable effects are limited in most patients despite the accumulation of intra-tumoral antigen-specific T cells. The tumor microenvironment (TME) is partly responsible for these failures through active blockade of local antitumor immune responses and facilitation of immune escape. Several immune modulating factors and/or cells are elicited within the TME, including the metalloproteinases, which enhance tumor growth and invasion through effects upon the tumor stroma, vasculature, and activation of factors such as TGF and TNF. Matrix metalloproteinase-2 (MMP-2), a gelatinase, is over-expressed in most cancers including melanoma, and its expression is associated with increased dissemination and poorer survival/prognosis. We recently found that enzymatically active MMP-2-conditioned dendritic cells (DCs) preferentially generate TH2 cells through mechanisms that inhibit IL-12 and up-regulate OX40L expression. Of note, only enzymatically active MMP-2 blocks IL-12 production, while both active and inactive conformations of MMP-2 induce up-regulation of OX40L. Strikingly, we also detected TILs in several patients that displayed MMP-2-specific responses. These responses were TH2-like and their presence was found to be inversely correlated with survival. MMP-2, therefore, acts simultaneously as an endogenous TH2 conditioner and tumor-associated antigen, which may explain, in part, the occurrence of unfavorable TH2 responses in melanoma. We previously characterized the mechanism responsible for IL-12 inhibition, which involves enzymatic cleavage of the type IIFN receptor, and consequent reduced STAT-1 phosphorylation and IL-12p35 transcription. We have since identified other novel immune mechanisms underlying MMP-2-dysregulation of DCs and the TME: MMP-2 directly triggers TLR-2 mediated signaling on both DCs and melanoma cell lines, inducing expression of OX40L and production of pro-inflammatory cytokines, respectively. In Aim1, therefore, we will first identify the relevant TLR receptors and signaling pathways involved in OX40L up-regulation. The clinical relevance of this novel finding will be tested in animal models of melanoma (Aim 2). Finally, in Aim 3, we will evaluate whether MMP-2 directly modulates melanoma function and growth via TLR-mediated pathways.